Experiments with chickens are proposed in which the following measurements will be made: loss of radiant energy; loss of energy by convection; oxygen consumption; production of carbon dioxide and water vapor; heart rate; hypothalamic, spinal cord, core and skin temperatures; the electromyogram to evaluate the extent of shivering. The measurements will be made under three temperature conditions, 10, 20 and 30 C, with constant humidity. In these series of experiments the hypothalamic preoptic temperature will be held constant at different temperatures and between 35 and 45 c whereas in the other experiments this temperature will not be controlled. Experiments in which biogenic amines are unfused into the third ventricle will also be carried out at 10, 20 and 30 C to determine the effect of these amines on the parameters metioned above. Experiments will be designed as randomized complete block designs so that the among animal variation can be assessed and removed from the random variation in the analysis of variance. The objectives are to investigate the details of a proposed tentative model for thermoregulation in the chicken by obtaining measurements of the physiological responses (above) as influenced by the thermal environment, and to use these data to develop the transfer characteristics of the controlling system.